Polishing pads, such as chemical mechanical polishing (CAMP) pads are widely used in a semiconductor manufacturing field to horizontally plagiarize various types of layers, such as oxide layers, nitrite layers, metal layers, etc. In one conventional arrangement, a CAMP pad is provided with a hole H. A chuck including a wafer to be plagiarized is placed in contact with the CAMP pad including the hole H. A slurry is provided on the polishing pad to facilitate the CAMP process and a light reluctance measurement unit is used to determine when the wafer has been sufficiently plagiarized. The end point of the polishing process is determined by the light reluctance measurement unit by measuring the light reflected through the hole or window H. However, the ability of the slurry to fall through the hole in the CAMP pad reduces the accuracy of the measurements made by the light reluctance measurement unit.
In another conventional device, the CAMP pad does not include a hole. In such an arrangement, the progress of the polishing cannot be monitored in-sit-up and a manufacturing delay is introduced when the wafer must be removed from the CAMP process to check the progress of the polish. In such a system, the end point of the polishing process may be determined utilizing a preset timing period. However, such systems are inherently inaccurate.
In yet another conventional device, a pad window is inserted in the hole of a top polishing pad. The pad window is made of a transparent material, which allows transmission of the laser beam. However, in the conventional device, the pad window sags in downwardly and/or an interface gap occurs between the top polishing pad and the window due to mechanical polishing pressure. As a result, slurry may accumulate on the top surface of the sagging pad window or slurry may leak through gaps in the side. Each of these causes scattering of the laser beam and degrades the transmission.